摘要:

We addressed the question of how rapidly gonadal steroids might affect behavior by studying how fast testosterone (T) could augment the actions of the striated penile muscles and their associated penile reflexes. Eight male rats, functionally castrated 4 months before this study, bore chronically implanted electrodes in the bulbospongiosus (bulbocavernosus) muscle. The males were observed for the display of penile reflexes immediately after the injection of T (250 µg i.m.) and T propionate (250 µg s.c), as well as after injections of only the oil vehicle. Overt penile responses were rare. However, in several tests subcutaneous twitching was observable near the midline posterior to the penis. These twitches were accompanied by electromyographic bursts and were attributed to contractions of the bulbospongiosus muscle. T reliably (p < 0.025) accelerated the onset of electromyographic activity: 6 of the 8 males had electromyographic bursts before the 30-min limit, and 3 males responded within 6 min. This is the first demonstration of such a rapid action of androgens on behavior or its basis in striated muscle activity. The rapid muscular response to T was ascribed to steroid-sensitive neuronal membrane receptors. Such responsiveness could increase the intensity of penile reflexes within minutes after surges of luteinizing hormone and T have been induced by cues associated with estrous females and thereby could contribute to the fertility of matin

ISSN:0028-3835    

DOI:10.1159/000125049

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Single and dual immunohistochemical staining techniques were used to assay the effects of disruption of brain stem catecholaminergic inputs on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) immunoreactivity in parvocellular neurosecretory neurons of the paraventricular nucleus of the hypothalamus (PVH) in normal and in adrenalectomized (ADX) rats treated with dexamethasone or vehicle. The results may be summarized as follows: (1) In adrenally intact rats, confirmed unilateral transection of ascending catecholaminergic pathways near their origins in the medulla produced a decrement in the number of CRF-immunoreactive cells that could be detected on the side of the brain ipsilateral to the cut. No effect on AVP immunoreactivity in the parvocellular division of the PVH was evident. Staining for both peptides in terminals in the external lamina of the median eminence tended to show modest decreases on the lesioned side of the brain. Compatible results were obtained in comparing the effects of bilateral transections with controls. (2) Unilaterally lesioned ADX rats treated with vehicle showed the expected enhancement in CRF immunostaining in the parvocellular division of the PVH, though the response on the side ipsilateral to the lesion was blunted relative to that seen contralaterally; the effect of ADX on AVP immunoreactivity on the ipsilateral side was more markedly reduced, but still showed evidence of enhancement (i.e., could be colocalized in some CRF immunoreactive perikarya). (3) Unilaterally lesioned ADX rats treated with dexamethasone showed no evidence of enhanced CRF or AVP immunoreactivity in perikarya or terminals on either side of the brain. The generally lower levels of staining for both peptides seen on the lesioned side across conditions suggest that the effect of interruption of ascending catecholaminergic pathways on peptide dynamics in the PVH is dissimilar to that of ADX, is manifested via different mechanisms, and that at least some types of feedback inhibition of corticotropin-releasing peptides by adrenal steroids do not require intact catecholaminergic inputs to be exhibited.

ISSN:0028-3835    

DOI:10.1159/000125050

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The existence of a growth hormone-releasing hormone (GHRH)-containing local neuronal network in the arcuate nucleus of the rat has been established on the basis of light and electron microscopic immunohistochemistry. GHRH-immunostained nerve terminals were demonstrated in synaptic contact with GHRH-immunoreactive dendrites and perikarya. These neuronal circuits may allow arcuate GHRH neurons to operate synchronously, or may provide morphological evidence for the existence of a neuronal ultrashort feedback mechanism for regulating GHRH release in the hypothalamo-hypophyseal system.

ISSN:0028-3835    

DOI:10.1159/000125051

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Modulation of lordosis behavior by stimulation of noradrenergic receptor subtypes was examined in ovariectomized, estradiol benzoate (10 µg)-primed guinea pigs. In the first experiment, subcutaneous administration of the alpha-2-noradrenergic agonist, UK-14,304 (0.01, 0.5, or 1.0 mg/kg, Pfizer Central Research), produced a significant increase in lordosis behavior when these animals were compared with estrogen-primed control animals injected with saline. In a second experiment, estrogen-primed animals were injected with the alpha-1-noradrenergic agonist methoxamine (0.5 mg/ kg, s.c), UK-14,304 (0.5 mg/kg, s.c), or both drugs given together. Methoxamine or UK-14,304 administered alone facilitated lordosis in fewer than 50% of animals (17 and 39%, respectively). However, when both drugs were given together, 76% of the animals became sexually receptive. A third experiment showed that lordosis behavior facilitated by UK-14,304 could be attenuated by the administration of the alpha-2-noradrenergic antagonist idazoxan (2.5 mg/kg, s.c). Only 29% of sexually receptive animals (i.e. those animals primed with estradiol benzoate plus UK-14,304) continued to show lordosis after they received idazoxan. The results obtained from these and previously reported experiments suggest that both alpha-1- and alpha-2-noradrenergic receptors are involved in the regulation of lordosis behavior in the guinea pig

ISSN:0028-3835    

DOI:10.1159/000125052

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Distribution and properties of receptors for gonadotropin-releasing hormone (GnRH) were analyzed in the brain of adult male rats. Binding of the iodinated GnRH agonist Des-Gly10-(D-Ala6)-GnRH ethylamide was studied in hippocampus and anterior pituitary using three convergent approaches: quantitative autoradiography on frozen tissue, binding to fresh slices, and binding to crude membrane preparations. In all cases, binding was specific, saturable, and time, pH, and temperature dependent. Quantitative autoradiography revealed that the density of binding sites was high in the stratum oriens and stratum radiatum of the CA1-CA4 regions of Ammon’s horn. The pyramidal cell layer was faintly labelled. Binding was almost undetectable in the dentate gyrus. The highest density of sites (Bmax = 11.6 + 1.0 fmol/mg protein) was observed in the stratum radiatum of the CA3 region. Under the same conditions the value obtained for pituitary tissues was 20.7 + 2.8 fmol/mg protein. Analysis of saturation curves indicated only one class of high-affinity sites for the hippocampus (CA3; Kd = 0.28 + 0.03 nM) and for the pituitary (Kd = 0.29 ± 0.08 nM). Both native GnRH and GnRH antagonist were potent competitors of binding. Fresh slices and membrane preparations from whole hippocampus confirmed these autoradiographic data and yielded affinity constants of 0.28 + 0.01 and 0.52 + 0.08 nM, respectively. In addition, a very high binding density was present in the amygdaloid complex, while binding was barely detectable in the hypothalamus. These results demonstrate that high densities of specific GnRH receptors are present in areas concerned with the regulation of behavioral functions. GnRH may thus be involved as a neurotransmitter in the integration of endocrine and behavioral reproductive process

ISSN:0028-3835    

DOI:10.1159/000125053

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Pituitary gonadotropin-releasing hormone (GnRH) binding sites were studied in persistent estrous rats. For comparison females at different stages of the estrous cycle, ovariectomized animals, and intact males were examined. Persistent estrus was induced by a hypothalamic knife cut, administering testosterone to neonatal rats, or by constant illumination. Rats showing spontaneously such alteration were also used in the experiment. Besides pituitary GnRH-binding sites, the GnRH content of the median eminence and plasma luteinizing hormone, follicle-stimulating hormone, estradiol, and progesterone concentrations were determined. Pituitary GnRH receptors changed during the estrous cycle with the highest concentrations observed on proestrus. In rats in persistent estrus, pituitary GnRH-binding sites varied between proestrous and estrous values of cyclic females. Ovariectomy resulted in a significant increase in receptors. Depending on how the persistent estrous syndrome was induced, very different amounts of GnRH were found in the median eminence of the various groups. Our data indicate that the GnRH-binding sites on pituitary cells of persistent estrous rats are in essence not changed.

ISSN:0028-3835    

DOI:10.1159/000125054

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Conscious mature and immature rats were administered either saline or an ethanol (ETOH)-saline solution via a permanent intragastric cannula, and plasma growth hormone (GH) levels were measured by radioimmunoassay of external jugular blood samples drawn every 10 min through an indwelling Silastic catheter. Control injections of saline into the gastric cannula did not modify plasma GH concentrations, whereas both groups of rats which were administered ETOH showed significant decreases in plasma GH concentrations and no evidence of the pulsatile secretion of the hormone. Comparable increases in the area under the GH curve occurred following a challenge dose of GH-releasing factor in both saline- and ETOH-injected rats, indicating that pituitary responsiveness was the same for both groups. These results indicate that ETOH is capable of altering GH secretion in adult as well as prepubertal animals, via an action at the hypothalamic level.

ISSN:0028-3835    

DOI:10.1159/000125055

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Growth hormone (GH) pulses in vivo are associated with increased hypothalamic portal growth hormone releasing hormone (GH-RH) concentration and can be prevented by GH-RH antisera. GH pulses are also associated with prior reduction of portal somatostatin (SRIF) concentrations, although SRIF antisera do not abolish GH pulses. In vitro, pulses of GH-RH as well as SRIF withdrawal are followed by pulses of GH release; the presence of GH-RH enhances post-SRIF GH release. We asked four questions: (1) During combined GHRH-SRIF exposure in vitro, must SRIF withdrawal be complete to produce a pulse of GH release, or is there a threshold diminution of SRIF which permits it? (2) When pulsatile GH release does occur, is it an all-or-none phenomenon, or is it titratable by fractional reduction of SRIF? (3) Does varying the GH-RH concentration while administering SRIF systematically alter GH release in response to fractional SRIF reduction? (4) Given a small but distinct effect of GH-RH on release of stored prolactin (PRL) in this system, does fractional SRIF reduction alter PRL release in parallel? Rat pituitary tissue whose hormone stores had been prelabeled with tritium was perifused for 120 min in combined 25 nM SRIF and 3 or 10 nM rat GH-RH (rGH-RH). Then, while maintaining rGH-RH concentrations, the SRIF concentration was left unchanged (control) or was reduced to 20, 15, 10, 5, or 0 nM for 60 min. Release of stored rGH and rPRL was assessed by immunoprecipitation. The amplitude of rGH and rPRL pulses was titrated by fractional SRIF reduction. The hormone release increased logarithmically as SRIF was reduced arithmetically. Altering the rGH-RH concentration shifted the response curve. Conclusion: known changes of hypothalamic portal GH-RH and SRIF concentrations can regulate the magnitude of pulsatile release.

ISSN:0028-3835    

DOI:10.1159/000125056

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The ionic conductance mechanisms underlying the action potential behaviour of frog melanotrophs in primary culture were studied by using the patch-clamp technique in whole-cell configuration. The action potentials spontaneously generated by these cells were predominantly sodium spikes with a calcium component. Voltage-dependent sodium, calcium, potassium and calcium-activated potassium currents were identified and analysed separately. The voltage-dependent sodium current was characterized by its fast kinetic, its low-threshold activation, its voltage-dependent inactivation and a tetrodotoxin sensitivity. Calcium currents were identified on the basis of their ionic selectivity to divalent cations (Ba2+, Ca2+, Co2+) and their time course. Only two of the three well-documented calcium currents could be detected in frog melanotrophs. A sustained calcium current (IcaS) and an inactivating calcium current (IcaN) were elicited by step depolarizations up to -20 mV. IcaN inactivated for membrane potentials more positive than -50 mV; its inactivation appeared to be both voltage- and calcium-dependent. Transient calcium current (IcaT) has never been observed. Two types of potassium currents were identified: voltage-dependent potassium (IĸV) and calcium-activated potassium currents, (Iĸ[Ca]). They were both suppressed by tetraethylammonium chloride, whereas only Iĸ(Ca) was blocked by cobalt. These major ionic currents underlying spontaneous electrical activity are assumed to be involved in the process of α-melanocyte-stimulating hormone release. The present study provides the ground for future investigations regarding the relationships between the electrical and secretory activities in amphibian pars intermedia ce

ISSN:0028-3835    

DOI:10.1159/000125057

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The indirect immunofluorescence technique was used to study the relation between corticotropin-releasing factor (CRF) and GABAergic neurons in the rat hypothalamic paraventricular nucleus (PVN). In colchicine-pretreated animals, glutamic acid decarboxylase (GAD)- and GABA-immunoreactive (IR) neurons were observed within the medial part of the parvocellular division of the PVN as well as surrounding the nucleus itself. In general, the GAD antiserum, as compared to the GABA antiserum, revealed stronger IR cells and a higher number of cells in the PVN. CRF-IR cells were observed throughout the whole rostrocaudal extension of the PVN, but predominantly in its dorsal medial parvocellular part. Adjacent sections stained, respectively, with antisera against CRF, GAD or GABA, revealed overlapping distributional patterns within the parvocellular part of the PVN. Employing a direct double-staining technique with sheep GAD and rabbit CRF antisera, it was demonstrated that both GAD and CRF immunoreactivities occurred in the same neurons, particularly in the dorsomedial aspect of the parvocellular PVN. GAD-positive neurons located in the ventromedial parvocellular PVN, periventricular nucleus and surrounding the PVN lacked CRF immunoreactivity. In addition, with an elution-restaining technique it was possible to demonstrate that also GABA immunoreactivity was present in some CRF neurons in the dorsomedial parvocellular PVN. Intravenous injection of the retrograde tracer Fast Blue resulted in labelling of neurons in the periventricular area and in both the parvocellular and magnocellular division of the PVN. After processing the sections for GAD/CRF immunohistochemistry, it was possible to demonstrate the presence of retrogradely labelled GAD/CRF cells, pointing at a PVN median eminence projection for these neurons. The present findings demonstrate that a subpopulation of the CRF-containing neurons in the parvocellular division of the PVN in addition are GABAergic, thereby indicating a possible corelease of these compounds, presumably in the median eminence. Possible interactions of GABA within the hypothalamo-pituitary-adrenal axis are discussed.

ISSN:0028-3835    

DOI:10.1159/000125058

出版商:S. Karger AG    

年代:1988

数据来源: Karger